Spin dryer having a shaded-pole motor



Dec. 19, 1967 Fllg.

Inventors: Warner Sowo. 3 S/Lggfried TELL/31in 5 46b: F Httovness w. SOWA ET AL 3,358,381 SPIN DRYER HAVING A SHADED-POLE MOTOR Filed July 28, 1965 United States Patent 3,358,381 SPIN DRYER HAVING A SHADED-POLE MOTOR Werner Sowa and Siegfried Tillner, Oldenburg in Oldenburg, Germany, assignors to Licentia Patent-Verwaltungs-G.m.b.H., Frankfurt am Main, Germany Filed July 28, 1965, Ser. No. 475,341 Claims priority, application Germany, July 29, 1964, L 48,407 16 Claims. (Cl. 3458) ABSTRACT OF THE DISCLOSURE A household laundry spin dryer composed of a rotatable drum mounted directly on the vertically-oriented shaft of a drive motor, the drum motor assembly being supported by a spring assembly, the motor being of the shaded pole type and serving to impart an increased acceleration to the drum over the lower portion of its speed range due to the fact that the motor is constructed so that its torque-speed characteristic is increased in this lower speed range at the expense of the motor breakdown torque, which occurs at the upper portion of the assembly speed range.

The present invention relates generally to household laundry spin dryers, and, more particularly, to a simplification and an improvement of such a device which has centrifugal speeds in the range of 1350 to 3000 revolutions per minute (r.p.m.).

Household laundry spin dryers are spin dryers which can be set up free standing and have a loading capacity of 2 to 5 kilograms of dry clothing. In accordance with known devices, the centrifugal drum is directly or indirectly mounted on the motor shaft and the assembly or unit formed by the motor and the centrifugal drum totical direction. Two and four-pole Single phase A.C. motors usually of the capacitor type are mainly used for driving such devices.

In the shaded-pole motor field, a simple one-phase A.C. motor having a short-circuited inductive or a low starting and accelerating torque, for example, table fans, heating fans, simple record players, and similar devices.

This is due to the starting characteristics of the shadedpole motor and its behavior during operation as well as to the special accelerating conditions in spin dryers with a spring providing an elastic mounting for the motor centrifugal drum assembly. This peculiarity lies in the limitation of the power output, in the type of construction resulting from the power output, and in the changing of direction of the load characteristics in dependence upon the power output of the motors.

Because of these technical factors, the four-pole shadedpole motor which has already been developed to have the desired performance characteristics has remained unsuitable for use as the drive for household laundry spin dryers. Only a special adjustment of this motor beyond the normal adjustment makes it usable. A two-pole shadedpole motor having the required performance characteristics is not yet known.

From the load characteristic of conventional four-pole shaded-pole motors and the characteristic of the household spin dryers, it can be seen that there are difliculties in accelerating to operating speed even when the motor is provided with a sufficiently high power rating. During operation, the centrifugal drum acts as a load on the motor only because of its rotational friction. The requirement for a certain accelerating time means that the acceleration torques which are to be produced are most important. For accelerating to running speed, the entire curve of the acceleration torque-speed curve from standstill to breakdown torque is of importance.

Shaded-pole motors having the power necessary for meeting the coming-to-speed time requirements, not only have a relatively low starting torque of below 0.5 of the rated or nominal torque, but also at about one third of the synchronous speed there is a pronounced reduction in the torque which is particularly caused by a third field harmonic which moves in the direction of rotation. During the acceleration or coming to speed of the spin dryer, the moment of inertia or flywheel moment increases considerably because of the outward displacement of the Wet laundry toward the walls of the drum. In addition to this, the motor-spin dryer assembly at this point passes through its critical rotational speed which is caused by the imbalance of the laundry. Because of this, considerable vibrations of the motor and the drum are caused, depending on the amount of imbalance and the time it takes to pass through its critical speed. The result of this is that the torque requirement for the spin dryer increases to exceed the torque provided by the motor, that is, the spin dryer does not increase its speed.

The problems for spin dryers having rotational speeds of about 1400 revolutions per minute with a four-pole shaded-pole motor can only be overcome by using special measures for the spin dryer and also particularly for the elastic suspension as well as by an extraordinary balancing off of the motor data. By increasing the number of revolutions per minute of the spin dryer in the two-pole arrangement to 2800 r.p.m., in order to improve the spin dryer,

is, characteristic is required.

Also, however, the two-pole shaded-pole motor permits its power rating to such an extent and to and in which the usual dip in speed of the motor is significantly obviated.

These objects and plished in accordance a motor-centrifugal drum assembly is elastically suspended and mounted with its axis in the vertical direction. The motor is a shaded-pole motor in which above all the torque-speed characteristic is raised in the lower r.p.m. range at the expense of the break-down torque to such an extent that the integral of the torque speed curve is by suitable construction of the short-circuited winding and of the rotor resistance in conjunction with high saturation.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a schematic partial sectional view illustrating the basic structure or" the spin dryer of the present invention.

FIGURE 2 is an elevational view of one of the stacked laminations of the stator of the two-pole drive motor.

With more particular reference to the drawings, it can be seen from FIGURE 1 that the motor 3 is suspended by means of spring members 4 from the bottom of the housing 1 of the spin dryer. The centrifugal drum 6 is mounted directly on the shaft of the motor. The motor is ventilated by two finned rotors 7 and 8. The assembly which comprises the motor and centrifugal drum is mounted so that it can swing or vibrate in all directions.

As shown in FIGURE 2, the stator of the two-pole shaded-pole motor is constructed of a stack of laminations each of which includes a generally rectangular yoke frame 9 and the ole laminations or pole stars 1%) which are inserted into the frame. The concentric field winding (not shown) is disposed about the pole shoes 11 and 12. The width 13 of the pole shoe is about one half of the pole lamination width 14. This pole lamination width 14 is about 1.1 times as large as the diameter 15 of the rotor opening. The restriction or narrow magnetic path which is provided in the connection-which represents the leakage web 16between the main pole portion 17 and the shaded pole portion 18 of the other pole, is provided by the slots 19 and 2% which open outwardly.

The tip 21 of the main pole is tapered from the main pole portion. This tapering is provided by a circular are 22 having its center 23 on the pole axis and at a distance of 1/6 of the rotor opening diameter from the center of the rotor opening and having a radius 24 which is one half of the width of the pole lamination. The length of this are from the startingpoint of the tip 21 of the main pole to the narrowest restriction is about four times the width of the starting point 25. This arc subtends an angle .of about 97. The slot 19 is disposed at an angle of 28 relative to the median perpendicular to the pole axis whereas the smaller slot is at an angle of 16 with respect thereto. Thus, a zone for the narrow magnetic path is provided which corresponds to an arc of 12. When it is considered that the split pole slot 26 which is adjacent to the pole axis is at an angle of 23 relative to the pole axis, and that the starting point of the tip of the main pole is disposed at an angle of 21 relative to the pole axis, then it can be seen that the arc subtended by the main pole is 129, the are for the shaded pole is 39, and the are for the zone of the narrow magnetic path is 12.

For the special drive means of the present invention, the point at which the breakdown torque occurs is of less importance than the entire acceleration or coming-tospeed curve of the motor and this is particularly the case in the lower r.p.m; range because of the exceptionally steep rise of the speed which is required when the device passes through the critical speed. In comparison to a normal motor which is designed for maximum torque, the resistance of the short-circuited auxiliary pole-the short-circuited winding must be decreased and the resistance of the squirrel cage in the rotor has to be increased and the motor has to have higher saturation.

A two-pole shaded-pole motor having distinctly defined poles is advantageously used in the present invention because of its higher r.p.m. The stack of laminations of the stator as has been seen from the above, includes a substantially rectangular yoke frame having a pole lamination inserted into it or a so-called pole star. This type of construction is most suitable for the embodiment of a two-pole shadedpole motor having those characteristics F output. The magnetic flux for the invention which permit the. needed increase of the power rating and the adjustment of the torque-speed curve. In addition to this, they are simple and economical. The amount of metal laminations required is smaller than when they are round-cut and the paths of the lines of force are'the shortest.

In the larger shaded-pole motors, the scattering conditions become very critical because of the higher number of ampere turns. They are partly responsible for the limitation of the power rating and therefore special attention must be given to the scattering paths. Critical scattering conditions occur at the scattering webs which are the magnetic connecting straps from the main pole to the shaded pole which is adjacent to it. As a result of the higher number of ampere turns, thefiux from the main pole portion to the shaded pole portion of the neighboring pole becomes too great, and has to be limited by a narrowing or restriction or a raising of the magnetic narrow path. This restriction can be obtained by making holes, or more advantageously by providing slots or grooves, in the tip of the shaded pole.

In accordance with the present invention, in order to prevent endangering the mechanical stability of the pole laminations, and also to obtain a defined zone of the slots, two or more slots are made which open outwardly. The Zone of the narrowing must not extend up 'to median perpendicular to the pole axis for otherwise the are for the main pole would become too small. The are for the shaded pole is thus smaller than 50. The favorable position and size of the narrow magnetic path which is provided by the constriction contributes to a lessening of the harmonic induction distribution in the air gap. The air gap between the back of the main pole and yoke has to be made wider with respect to motors having smaller which would flow as a result of the high saturation would be a real loss since it does not contribute to the generation of torque as does the scattering flux from one pole tip to the other. Therefore, the distance betwen the yoke and the back of the pole, that is, the back of the pole tip, has to be relatively large. In accordance with the invention, it should not be smaller than one tenth of the diameter of the rotor opening. The necessary continuous tapering of the pole tip of the main pole also satisfies this requirement. The approximation of the field strength distribution in the air gap to the sinusoidal form which is obtained and especially the third harmonic, is suppressed. This harmonic causes the dip in the accelerating curve.

In accordance with the invention, this tapering is provided by a circular are which has its center on the axis of the pole and at a distance from the center of the rotor opening which is about of the diameter of the rotor opening. It has a radius which is equal to /2 of the width of the pole laminations and this width is about 1.1 times as large as the diameter of the rotor opening.

The pole width is about one half of the diameter of the rotor opening and provides a certain width for the starting point of the pole tip at the main pole. In accordance with the invention, the length of the pole are from its starting point to the constriction is arranged to be about four times as large as the width of the starting point. This arc subtends an angle of 97. The are of the shaded pole is thereby reduced in favor of the arcof the main pole and the power loss is thus reduced. An arc subtending an angle of less than 50 is thus provided for the shaded pole. The power loss of the shaded pole is further reduced by a conductor cross section of the shaded pole windings which is small compared to those of smaller motors. The shaded pole slot which is adjacent to the axis of the pole is disposedsubstantially at the point where the tip of the pole starts. In order toeliminate shaded pole sl'ot scattering and the'shaded pole slot is open. A sufficient phase displacement is obtained by such an arrangement as are considerably great starting and acceleration torques.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

What is claimed is:

1. A spin dryer comprising,

a housing;

a shaded pole motor having a drive shaft extending vertically therefrom, said motor including a rotor and a short circuited winding, said short circuited winding and the resistance of said rotor, in conjunction with high saturation being arranged so that the torque-speed characteristic is raised in the low speed range and at the expense of the breakdown torque to such an extent that the integral of the torquespeed characteristic is substantially equal to the integral of the torque-speed characteristic of a motor which is constructed to have a maximum breakdown torque;

a centrifugal drum mounted on said drive shaft and defining an assembly therewith; and

spring means for vertically suspending said assembly in said housing.

2. A dryer as defined in claim 1 wherein said motor is a two pole shaded-pole motor.

3. A dryer as defined in claim 2 wherein said motor includes a stator constructed of a stack of laminations each in the form of a generally rectangular yoke frame and having a pole lamination disposed in the frame.

4. A dryer as defined in claim 3 wherein the width of the poles is about one half of the width of the pole lamination.

in combination:

of the tip of the main pole is continuously tapered from its starting point to the median perpendicular to the pole axis.

6. A dryer as defined in claim 5 wherein each lamination is provided with a rotor opening, the tapering being provided by a circular arc having its center on the pole axis at a distance of about of the rotor opening diameter from the center of such opening and a radius which is about one half of the width of the pole lamination.

7. A dryer as defined in claim 6 wherein the length of the inner circular arc of the tip of the main pole is about four times as long as the width of the starting point of the tip of the main pole.

8. A dryer as defined in claim 3 wherein each lamination defines two main poles and two auxiliary poles, a connection strip disposed between the tip of each main pole and the tip of the auxiliary pole associated with the other main pole, said connection strip providing a constriction and a narrow magnetic path beyond the median perpendicular to the pole axis.

9. A dryer as defined in claim 8 wherein at least two outwardly opening slots define the narrow magnetic path.

10. A dryer as defined in claim 9 wherein a slot is provided to define each shaded pole, said outwardly opening slots being of different size and depth with the larger and deeper of the slots being disposed closer to the shaded pole slots.

11. A dryer as defined in claim 9 wherein a slot is provided to define each shaded pole, the narrow magnetic path formed by the slots subtends an angle from 16 to 28 relative to the median perpendicular to the pole axis and considered in the direction of the shaded pole slots.

12. A dryer as defined in claim 3 wherein there is more than one open shaded pole slot.

13. A dryer as defined in claim 12 wherein the shaded pole slot which is closest to the pole axis is at a distance from this axis which subtends an arc of about 23.

14. A dryer as defined in claim 5 wherein the starting point of the tip of the main pole is disposed at a distance from the pole axis which subtends an arc of about 21.

15. A dryer as defined in claim 3 wherein the main pole subtends an arc of about 129 and the shaded pole subtends an arc of about 38.

16. A dryer as defined in claim 9 wherein the main pole subtends an arc of about 129, the shaded pole subtends an arc of about 39, and the narrow magnetic path subtends an angle of about 12.

References Cited UNITED STATES PATENTS 1,071,956 9/1913 Psarski 3458 2,827,583 3/1958 Hoddy 310-172 FOREIGN PATENTS 751,554 6/1956 Great Britain. 956,610 4/ 1964 Great Britain.

FREDERICK L. MATTESON, JR., Primary Examiner. D. A. TAMBURRO, Assistant Examiner. 

1. A SPIN DRYER COMPRISING, IN COMBINATION: A HOUSING; A SHADED POLE MOTOR HAVING A DRIVE SHAFT EXTENDING VERTICALLY THEREFROM, SAID MOTOR INCLUDING A ROTOR AND A SHORT CIRCUITED WINDING, SAID SHORT CIRCUITED WINDING AND THE RESISTANCE OF SAID ROTOR, IN CONJUNCTION WITH HIGH SATURATION BEING ARRANGED SO THAT THE TORQUE-SPEED CHARACTERISTIC IS RAISED IN THE LOW SPEED RANGE AND AT THE EXPENSE OF THE BREAKDOWN TORQUE TO SUCH AN EXTENT THAT THE INTEGRAL OF THE TORQUESPEED CHARACTERISTIC IS SUBSTANTIALLY EQUEL TO THE INTEGRAL OF THE TORQUE-SPEED CHARACTERISTICS OF A MOTOR WHICH IS CONSTRUCTED TO HAVE A MAXIMUM BREAKDOWN TORQUE; A CENTRIFUGAL DRUM MOUNTED ON SAID DRIVE SHAFT AND DEFINING AN ASSEMBLY THEREWITH; AND SPRING MEANS FOR VERTICALLY SUSPENDING SAID ASSEMBLY IN SAID HOSING. 